U.S. investment fund Blackrock Inc and other investors have built stakes in Spanish telecom operator MasMovil in the days after the filing of a formal bid on June 1, according to the Spanish stock market regulator.

Since KKR, Cinven and Providence launched a 2.96 billion euro (2.63 billion pounds) offer, MasMovil stock has been trading above the 22.50 euro implied share price, suggesting investors expect rival bids or a sweetened offer from the funds.

Between June 2 and June 5, Blackrock gradually raised its stake in MasMovil to 6.49% from 5.70%, while Sand Grove Opportunities Management, Simon Davies, Wellington Management all bought shares in MasMovil in early June, according to data released on Tuesday by the regulator.

On June 4, French telecom giant Orange said it would not file a counter bid for MasMovil.

The private equity trio said holders of 29.56% of MasMovil's stock had already agreed to sell at the price they offered. These shareholders have committed to remain loyal to the offer in the case of any counter bid lower than 26 euros.

(Reporting by Inti Landauro and Joanna Jonczyk-Gwizdala, editing by Louise Heavens)